The proposed work concerns the development of methods of characterizing and quantitating regional flows in the coronary vascular bed. The first aim is to provide a mathematical characterization of the transport (delay, dispersion, skewness) of an intravascular indicator through individual pathways in the coronary bed by using the combined approaches of microsphere deposition to estimate regional myocardial flow and of parallel pathway analysis to characterize the transport process between input and output, from which points simultaneous dilution curves will have been recorded. This will be extended to the simultaneous use of a flow-limited, permeating tracer, iodoantipyrine, to attempt to estimate the heterogeneity of local extravascular to intravascular volumes or local flow-to-volume ratios. The second aim is to study these transport characteristics and volume ratios in pathophysiological states in dogs with regional ischemia or raised LV end-diastolic pressures. The third aim is to attempt to apply the approach to data obtained by external gamma-detection, residue function curves, instead of from pairs of input-output dilution curves. Although fine temporal and spatial resolution are not likely achievable, the probability is that combinations of the mathematical approach with improved methods of localization of intramyocardial content of tracer will yield useful information leading toward good quantitation in estimating regional flows. BIBLIOGRAPHIC REFERENCES: Bassingthwaighte, J.B.: Approaches to modeling radiocardiographic data: Comments on F. Castellana's modeling of the central circulation. In: "Quantitative Nuclear Cardiography," ed. R. Pierson et al., J. Wiley & Sons, N.Y., 1975, pp. 226-230. Bassingthwaighte, J.B. and Holloway, G.A., Jr.: Estimation of blood flow with radioactive tracers. Sem. Nuc. Med. 6:141-161, 1976.